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There are great opportunities for genetic improvement in recently domesticated aquaculture species. However, the lack of appropriate tools limits the application of advanced techniques including the mapping of quantitative trait loci (QTL) and marker-assisted selection (MAS). The recent development of a genetic linkage map for the European sea bass allows the application of such methods for the first time in this species. We report a pilot trial of QTL mapping in a commercial sea bass population as a precursor to the application of MAS. Fertilized eggs collected on a single spawning day produced a population composed of a few large families. Fish were grown under commercial conditions, slaughtered at approximately 470 g and measurements were taken for several traits. Parentage analysis showed that the population consisted of 26 full sib families, with a common dam and several sires. Seven microsatellite markers spanning the largest linkage group (LG1) were then genotyped in 27 parents and their 422 progeny, in order to perform a QTL scan using half-sib interval mapping approaches. Significant QTL affecting six morphometric traits including length and depth, are reported. The success of the procedure demonstrates that QTL analysis can be applied in this species and will contribute to the study and future improvement of traits associated with production, profitability and sustainability.

Microsatellites represent codominant molecular genetic markers, which are ubiquitously distributed within genomes. Due to their high level of polymorphism, relatively small size and rapid detection protocols, these markers are widely used in a variety of fundamental and applied fields of life and medical sciences. In the field of aquaculture, microsatellites represent workhorse markers, which are useful for the characterization of genetic stocks, broodstock selection, constructing dense linkage maps, mapping economically important quantitative traits, identifying genes responsible for these traits and application to marker-assisted breeding programmes. In this review, genomic distribution, function, evolution and practical applications of microsatellites are considered, with special emphasis on fish genetics and aquaculture.

White Spot Syndrome Virus (WSSV) has decimated the shrimp aquaculture around the world. Breeding efforts to generate resistant stocks are necessary but there is a lack of basic information on challenge test strategies focused on genetic selection. Infection routes and developmental stages were evaluated on Penaeus vannamei as a first step in a strategy to select white spot virus (WSSV)-resistant stocks. Mortalities could not be induced before the PL30 stage. The impact of infection by immersion and blended tissue was intermediate on mortalities when compared to the minced tissue treatment on PL30. Blended and minced tissue treatments produced the highest mortalities on PL40 while immersion was intermediate. A general tendency towards higher susceptibility associated with older stages was detected. Additionally, juveniles of 1 g average weight from three local breeding programs were challenged. There were no differences in survival between the programs, although two of them derived their progenies from survivors of strong WSSV events. The implications of these results to the WSSV epidemiological characteristics and breeding programs are discussed.

We report the construction of sex-specific linkage maps for the white shrimp Penaeus (Litopenaeus) vannamei (Penaeidae; Crustacea). Linkage information was generated using amplified fragment length polymorphism (ATLP) markers in a mapping panel consisting of 42 individuals derived from a commercial cross. We used 103 primer combinations that produced 741 segregating bands. From them, 477 segregated in a 1:1 model, 181 in a 3:1 model. 62 fitted both models and 21 fitted neither model. A total of 394 loci with a 1:1 segregation ratio were mapped to unique positions in the male and female maps using a pseudotestcross strategy. A total of 51 and 47 linkage groups were detected for the male and female maps respectively, in comparison to 44 haploid groups expected from the karyotype. The female map covered 2771 Kosambi units (cM) and was 24% longer than the male map (2116 cM long). The distribution of the mark-m showed that both maps had low saturation and clustering at short linkage distances. Markers with a distorted segregation were observed as previously reported in other shrimp species. The estimated genomic length indicates that the P. vannamei genome has higher recombination rates than closely related species. We demonstrate the feasibility of implementing molecular techniques at low cost without the need of specialized equipment in a species that is at the initial stages of domestication. (C) 2004 Published by Elsevier B.V. ispartof: Aquaculture vol:242 issue:1 pages:105-118 status: published

Gynogenesis is thought to be a useful method to generate fully inbred lines in teleost fish. Endomitosis, which refers to the inhibition of first mitosis, should lead to fully homozygous offspring. In this study, the optimal conditions to induce mitogynogenesis (endomitosis) by heat shocking of the eggs were determined in the African catfish Clarias gariepinus. Comparable survival rates were obtained with a shock of 40°C applied for 1 min and a shock of 39°C applied for 1.5–2 min. Applying the shock around 20 or 37 min after activation resulted in the highest survival rates (ca. 5% relative to the positive control). The amount of inbreeding (homozygosity) and paternal contamination were assayed by using polymorphic microsatellite DNA markers. In less than 1% of the offspring paternal alleles were present, indicating a true gynogenic background for most of the progeny. Meiogynogenetic and mitogynogenetic C. gariepinus showed a fair amount of residual heterozygosity (respectively 86% and 75% for one of the markers). Heterozygous catfish obtained through mitogynogenesis were attributed to the (simultaneous) presence of meiogynogens. In addition, we prove that the sex determining system of African catfish C. gariepinus is heterogametic in the male (XY/XX).

Selection of fish has been constrained by the difficulties of communal raising due to the lack of a reliable tag for small fish. We have overcome this problem by the mixed rearing of the progeny of a complete 4×4 factorial cross of African catfish (Clarias gariepinus) in a single tank and microsatellite DNA fingerprinting a subsample at 1 month and 9 months of age. Simultaneously, these fish were scored for several phenotypic traits. Eighty five to 91% of all fish were identified uniquely on the basis of nine microsatellite DNA markers. The survival rate was affected by dam at 9 months of age. Dam and family effects were prominent in all phenotypic traits measured at 1 month of age, while sire and family effects were prominent at 9 months of age. Selection of the best growers on the basis of mass selection or family selection did not affect genotype probably because of the limited genetic background of the broodstock. Phenotypically, growth rate of the mass-selected group turned out to be higher than the family-selected group.

Meiogynogenesis of the African catfish (Clarias gariepinus) was optimized by altering the intensity, duration and timing of application of pressure, heat or cold shocks shortly after activation of the egg with sperm which had been genetically inactivated with UV irradiation. The distributions of the survival rates showed a unimodal (heat and hydrostatic pressure shock) or bimodal (cold shock) pattern and were specific to each treatment. The timing of the expulsion of the second polar body invariably occurred 3 to 5 min after fertilization. Of the three methods tested, cold (5°C, during 40 min at 3 min post-activation) and pressure (55.00 MPa during 2 min at 3 min post-activation) shocks turned out to be the most efficient in terms of survival rate. A relative hatching rate of up to 81% of gynogenetic diploid fish was achieved. The final proof of gynogenetic status was made with a paternity test by means of multiple-locus DNA fingerprinting.

The BASSMAP consortium, funded by the European Union, has been set up to improve the understanding of the genome of European sea bass (Dicentrarchus labrax). The specific aim is to locate genes of known function on the physical map and to compare specific regions among perciforms. We have produced an F1 cross of outbred sea bass as mapping panel and a Bacterial Artificial Chromosome library (7× redundancy and 165 kb average insert size). End sequencing of the BAC library is in progress and a radiation hybrid panel is under construction.